The magnetic encoder device used to detect the rotating speed (number of rotations) of a rotating body has a variety of number of applications and is composed of: a magnetic encoder including an annular fixing member for attachment to the rotating body and an annular magnet member that is fixed to the fixing member and has N and S poles magnetized circumferentially at regular intervals in a multipolar manner; and a sensor that is attached to a non-rotating body so as to be opposed to the magnet member for detecting rotation of the magnet member.
When the magnetic reading diameter of the sensor is small for a rotating body to which an axial-type magnetic encoder is to be attached, a magnetic encoder used is configured such that an annular fixing member to be fitted to the rotating body is formed by a cylindrical part and an inward flange part that is extended radially inward from an end edge of the cylindrical part, and the annular magnet member is fixed to the inward flange part (for example, refer to Patent Document 1, FIG. 3, and Patent Document 2, FIGS. 1 to 13. Hereinafter, referred to as “inward flange-type magnetic encoder”).